The article author Neerav Bhatt writes, “We take the availability of Global Positioning Systems (GPS) for granted as a ‘free’ service. But this constellation of more than two dozen satellites has been available to the public for less than 20 years, and has operated at the current degree of accuracy for just over a decade.” The rest of this very interesting article, and how it relates to Geocaching, can be found on his RAMBLING THOUGHTS BLOG
What a lot of people do not know, and the article does not mention, is there are TWO GPS signals. The two signals are Standard Positioning Service (SPS) and Precise Positioning Service (PPS). PPS is an encrypted signal for military and aviation use and important because the SPS is easy to spoof and jam. When the military uses PPS no enemy force can jam or spoof the much needed GPS signal.